Her high-pitched yapping is never likely to intimidate Japan's criminal fraternity, and few believe she would be able to lick them into submission or flash her dewy brown eyes to elicit a confession.

Instead, Momo, who weighs in at a mere 3kg (6.6lb), today became what is thought to be the first chihuahua - the world's smallest breed of dog - to qualify for police duty, as a search-and-rescue specialist.

The seven-year-old long-haired chihuahua - whose name means peach - was one of 32 out of 70 candidates to qualify as a search-and-rescue dog employed by police in Nara prefecture, western Japan.

What she lacks in her ability to terrify suspects into submission she makes up for in her sense of smell: Momo passed the test by finding a "trapped" victim of a simulated natural disaster in less than five minutes, having only sniffed his hat moments earlier.

Nara's prefectural police department operates an equal opportunities canine employment policy, but officials admitted that Momo's elevation to the ranks of police dog had taken them by surprise.

"Any breed of dog can be entered to become a police dog in the search-and-rescue division," a police spokesman told Reuters. But he added: "It's quite unusual."

While she has yet to rescue a single soul, Momo has already won a place in the affections of this nation of dog-lovers. Television footage showed her bounding through the grass, her long coat swaying in the breeze. "The phone hasn't stopped ringing all afternoon" with calls from smitten viewers, the spokesman said.

In January, Momo will get down to the more serious business of locating people buried under the rubble after earthquakes, making the most of her diminutive stature to squeeze into gaps inaccessible to bigger rescue dogs, such as retrievers and german shepherds.